MPEG is a name of an international organization for standardization of digital signal compression. Although they started discussing about MPEG in 1988, just a few experts recognized the term until the research of HDTV were activated in early 90's.
Today, realizing devices using MPEG moving picture compressing method such as DVD,digital TV, the term MPEG became common. In this multimedia era, anyone with a little interests in the field easily can hear or see the term, MPEG.
The MPEG became a widely known international standard, and it is remarkably succeeded in digital video signal processing rather than digital audio signal processing. There are existing one-chip MPEG decoders, and more various compressed moving picture media using MPEG compressing method will be developed. are existing one-chip MPEG decoders, and more various compressed moving picture media using MPEG compressing method will be developed.
FIG. 1 is a block diagram showing a decoding process of a MPEG decoder.
In variable length decoding (101), variable length coded DCT coefficient(Discrete Cosine Transform coefficient) is decoded.
Inverse scanning (102) is a procedure of converting a decoded one-dimensional DCT coefficient to a two-dimension form using a zig-zag or alternative scanning method. Any other scanning method can be also used.
Inverse quantization(103) is the procedure for getting inverse-quantized DCT coefficients, and includes saturation and mismatch control algorithm. Since MPEG only specifies requirements for decoding, not for encoding, saturation and mismatch control algorithms are meant to prevent accumulation of errors in case of mismatch between DCT of encoder and IDCT of decoder.
DCT coefficients produced in inverse quantization process(103) go through an IDCT process, and are fed to motion compensation process (105). Motion compensation process uses motion vector to improve efficiency of prediction. Motion vector is offset of previous or next reference field or frame.
IDCT of MPEG2 can be expressed in the following equation (1). ##EQU1##
where
x(i, j) (i, j=0, 1, 2, . . . , N-1) are pixel data, X(u, v) (u, v=0, 1, 2, . . . , N-1) are inverse quantized DCT coefficients.
In equation 1, N.sup.4 multiplications are needed to carry out a two-dimensional IDCT.
Since multiplier takes a lot of space in actual hardware and multiplication takes more clocks, this problem should be required to be solved.